Simultaneous isolation of cellulose and lignin from wheat straw and catalytic conversion to valuable chemical products

XRD
Figure 
3
 shows the XRD patterns of EWS and cellulose 
isolated from wheat straw. The peak at 22.4° of (002) 
reflection is attributed to the typical crystal lattice of cel-
lulose I
β
, which presents in every plot. It indicates that all 
samples exhibit the diffuse characteristic pattern of an 
amorphous phase [
33
]. A shoulder peak at 16.1° of (101) 
reflection and a weak peak at 34.2° of (040) reflection 
appears in the EWS pattern (curve a), which are attrib-
uted to cellulose phase. Compared to the pattern of EWS, 
there is no obvious change in the pattern of cellulose 
obtained at lower temperature and acid concentration 
(curve b). However, new diffraction peaks are observed 
in curve c, revealing that the phase structure of cellulose 
isolated at higher temperature and acid concentration 
becomes more complex. Broad diffraction peaks related 
to carbon appeared at 25.3° and 42.5° are also observed 
[
34
]. The former and the latter are assigned to the plane C 
(002) reflection [
35
] and (100/101) reflection of graphitic 
and/or organized carbon [
36
], respectively. These results 
indicate that cellulose is doped with charcoal, possibly 
derived from humins, leading to the formation of carbon 
fibers at higher temperatures and catalyst concentration 
[
37
]. Moreover, amorphous phase, with minor peaks at 
19.8°, 26.5°, 36.4° and 50.5° attributed to the presence of 
mineral SiO
2
, is observed in curve c [
38
]. These results 
are consistent with the IR spectrum of cellulose isolated 
at higher temperature and acid concentration, as shown 
in Fig. 
1
c–e. Both the IR and XRD results show that the 
removal of ash, mainly composed of SiO
2
, becomes diffi-
cult at a higher catalyst amount and temperature. It could 
be ascribed to the formation of carbon fibers, leading to 
ash adsorption on the surface of sample due to its excel-
lent adsorption properties [
39
, 
40
].
SEM
The morphologies of EWS, cellulose isolated from wheat 
straw under various conditions are observed using SEM. 
The SEM images in Fig. 
4
show that all samples display 
irregular and featureless image with a thick sheet-like 
structure. There is almost no difference in the image of 
EWS and cellulose obtained at lower temperature and 
Fig. 3 XRD patterns of (a) EWS, (b) cellulose isolated at 150 °C with 
1.0 wt% H
2
SO
4
and (c) cellulose isolated at 180 °C with 1.5 wt% H
2
SO
4

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Page 6 of 13
Yu et al. Appl Biol Chem (2021) 64:15 
acid concentration (Fig. 
4
b). However, a large number 
of surface attachments are observed in the image of cel-
lulose samples obtained at higher temperature and acid 
concentration (Fig. 
4
c). It also could be ascribed to the 
promotion in ash adsorption because of the formation of 
carbon fibers [
40
], as shown in the IR spectrum (Fig. 
1
d) 
and XRD pattern (Fig. 
3
c).